remove documents

This adds the functionality to delete documents.

Documents can be deleted only by the owner no matter
the visibility level.

A popup is shown to confirm the deletion.

If there is another user editing the document, he 
will see a popup warning him that the document has
been deleted and it will redirect the user to home.

I have also added another the functionality to broadcast 
the change of the document title. So while editing a
document, if someone change its title you will see the new 
title inmediately without refresh.